Improved laser beam shapes for DED-LB/M: low-fidelity Monte-Carlo design and high-fidelity verification

Complex beam shapes, i.e. laser beam intensity distributions, have shown great potential in laser processing technologies, with ring-profiles being widely investigated for additive manufacturing (AM), aiming to improve productivity, reduce defects and improve process stability. The question arises, however, whether the ring-profile is optimal, or rather, what laser beam intensity distribution could optimise different aspects of AM? Laser-directed energy deposition (DED-LB/M) is used in applications such as turbine blade repair, but is expensive and struggles with microstructural inhomogeneity. Recently, computationally-intensive simulations have been tested to design complex beam shapes for laser-powder bed fusion (PBF), only a few beam shapes, however, have been tested in DED-LB/M. This work focusses on DED-LB/M and proposes a novel methodology, using a Monte-Carlo approach to establish new improved laser beam intensity distributions. A low-fidelity model is subsequently used to calculate the resulting temperature fields. Example beam shapes are shown, aiming to improve process stability, to control the microstructure (through the thermal gradient) and to increase the process productivity. Next, validated high-fidelity simulations are used to verify the newly designed intensity distributions and show that the trends in peak temperature as well as melt-pool length and width are accurately captured by the low-fidelity model. The improved beam shapes predicted by the low-fidelity model will be used to direct future work, providing a starting point for intensity distributions to be experimentally tested. The low computational complexity of the low-fidelity model makes this methodology time-feasible, and its flexibility allows for new melt pool features to be improved. Consequently, this methodology can be transferred to further laser processes, such as surface-hardening or PBF, allowing for step-change improvements across the breadth of laser processing techniques.